1. Field of the Invention
This invention relates to a fan coupling for an engine of a vehicle which controls the rotational speed of a cooling fan of a water-cooled engine according to the temperature of the air passed through the radiator and the temperature of the cooling water.
2. Description of the Related Art
A conventional fan coupling for an engine of a vehicle is disclosed in Japanese Patent Laid Open No. 61(1986)-79032. The fan coupling for an engine of a vehicle comprises a housing separated into an operating chamber and a storing chamber by a separating plate. A rotor which includes a first torque transmitting portion on one side thereof and a second torque transmitting portion on the other side thereof is disposed in the operating chamber. The separating plate includes a first passage which communicates the first torque transmitting portion with the storing chamber and the second passage which communicates the first torque transmitting portion with the second torque transmitting portion. Both the first passage and the second passage are opened and closed by a single valve member which is formed into a plate-shaped configuration.
The valve member is operated by the temperature of the air passed through an radiator of a water-cooled engine and the temperature of the cooling water. When the temperature of the air passed through the radiator is raised to a predetermined value after warming up of the engine, the valve member is rotated by a bimetal element disposed outside of the housing in order that only the first passage may be opened in proportion to the rotation angle of the bimetal element. Therefore the storing chamber is communicated with the first torque transmitting portion in the operating chamber. Because the rotational torque of an input member connected with the rotor is transmitted to the housing through the first torque transmitting portion, the cooling fan fixed to the outer periphery of the housing is rotated slowly.
Later when the temperature of the cooling water is raised to a predetermined value, the valve member is raised by the expansion of a thermowax which is heated by the cooling water. Therefore the second passage is also opened. Consequently the storing chamber is communicated with both the first torque transmission portion and the second torque transmitting portion. Because the rotational torque of the input member is transmitted to the housing through both the first torque transmitting portion and the second torque transmitting portion, the cooling fan is rotated rapidly.
However because the entire second passage of the conventional fan coupling for an engine of a vehicle is opened at one time by the expansion of the thermowax, the rotational speed of the cooling fan is increased rapidly and it is impossible to control the rotational speed of the cooling fan in proportion to the temperature of the cooling water.
Japanese Utility Model Laid Open No. 56(1981)129620 discloses a fan coupling for an engine of a vehicle which comprises a valve member. The valve member is supported on a rotor by a pair of guides and closes openings disposed on the rotor. The valve member is connected with a rod which is slidable by expansion or shrinkage of a thermowax. By expanding the thermowax the valve member opens the openings.
However the valve member of the fan coupling does not gradually open the openings. Therefore the rotational speed of the cooling fan disposed on the fan coupling is increased rapidly.